1. Field of the Invention
This invention relates generally to methods and apparatus for determining the viewing/listening habits of the public, and more particularly to an improved ultrasonic, pulse-echo method and apparatus for determining the number of persons in the audience and the composition of the audience of a radio receiver and/or a television receiver.
2. Description of the Prior Art
Manual systems for determining the viewing/listening habits of the public are prone to inaccuracies resulting from the entry of erroneous data that may be intentionally or unintentionally entered and are slow in acquiring data.
U.S. Pat. No. 3,056,135 to Currey et al. issued Sept. 25, 1962 and assigned to the same assignee as the present application describes a method and apparatus for automatically determining the listening habits of wave signal receiver users. The method disclosed in Currey et al. provides a record of the number and types of persons using a wave signal receiver by monitoring the operational conditions of the receiver and utilizing both strategically placed switches for counting the number of persons entering, leaving and within a particular area and a photographic recorder for periodically recording the composition of the audience. A mailable magazine provides a record of both the audience composition and the receiver operation information for manual processing by a survey organization.
Various arrangements have been heretofore proposed for detecting motion utilizing an ultrasonic detection system. Such ultrasonic arrangements are shown, for example, in Iiea et al. U.S. Pat. No. 4,057,779, Kondo U.S. Pat. No. 4,213,196, and Salem U.S. Pat. No. 4,229,811. Other known ultrasonic systems are used for displaying images resulting from detected reflected waves.